Question

In the Langmuir Isotherm, following statements are true except one

• A. Adsorbed layer is uniform all over adsorbent
• B. No desorption takes place when the gas strikes solid surface
• C. No interaction between the adjacent adsorbed molecules takes place
• D. The layer of the gas adsorbed on the solid adsorbent is one molecule thick

Answer 1

The Correct Option is B

The Langmuir Isotherm is a model that describes the adsorption of molecules onto a solid surface. It assumes that:

• The surface contains a finite number of identical sites where adsorption can occur.
• Each site can accommodate only a single molecule, meaning the layer of adsorbed gas is one molecule thick.
• Adsorbed molecules do not interact with each other.
• The adsorbed layer is uniform all over the adsorbent surface.

Let us analyze each option provided in relation to these assumptions:

1. Adsorbed layer is uniform all over adsorbent: This aligns with the Langmuir Isotherm, which assumes a homogeneous surface where each site is equivalent.
2. No desorption takes place when the gas strikes solid surface: This statement is incorrect. The Langmuir Isotherm considers a dynamic equilibrium between adsorption and desorption. When a gas molecule strikes the surface, it can adsorb or desorb based on this equilibrium.
3. No interaction between the adjacent adsorbed molecules takes place: The Langmuir model assumes non-interacting adsorbed molecules, making this statement true according to the model.
4. The layer of the gas adsorbed on the solid adsorbent is one molecule thick: This is a basic assumption of the Langmuir Isotherm, thus this statement is true.

Therefore, the statement that is not true according to the Langmuir Isotherm is: No desorption takes place when the gas strikes solid surface. This contradicts the dynamic nature of adsorption and desorption in the model.